The chlamydial major outer membrane protein is the most abundant surface protein on C. trachomatis and its well-defined sequence variability accounts for the separation of C. trachomatis isolates into 18 distinct serovars. C. trachomatis MOMP also confers structural rigidity to the infectious form of the organism and exhibits characteristics consistent with porin activity. Evidence also exists to suggest that MOMP may contribute to chlamydial invasion into susceptible eukaryotic host cells, yet little is known regarding the conformational features of this molecule. The goals of the work proposed in this application are to determine the location of intra- and intermolecular MOMP disulfide bridges and establish the conformational features of surface exposed MOMP epitopes using site-specific mutagenesis and molecular modeling techniques.